This research proposal is designed to evaluate the transport relationships between the major anions of the glomerular filtrate, chloride, bicarbonate and phosphate, both under control circumstances and during experimental maneuvers of various kinds. In particular, it is planned to evaluate the rates of absolute and fractional chloride and bicarbonate, as well as phosphate, transport as these rates are affected by parathyroid hormone, thyrocalcitonin, volume expansion, and various diuretic agents. Furthermore, those factors which are paramount in regulating proximal anionic transport will be identified, and the mechanism by which they influence electrolyte transport will be studied. The effect of these agents on the unidirectional flux rates (tubule-to-peritubular and peritubular capillary-to-lumen) will be evaluated. Utilizing these avenues of approach, an attempt will be made to develop a single unifying hypothesis regarding the mechanisms of anionic transport in the proximal tubule.